The broad objective of this project is a continuing study of the demographic transition in a developing country, Taiwan, with special attention to fertility and the role of the family planning program. Procedurally, aggregate social changes as well as changes among individuals are analyzed, and many data sources and techniques are employed. Specific studies proposed or in progress include: a) Analysis of trends in desired family size, use of contraception, and fertility for couples with different socioeconomic characteristics. b) Tests of the relation of newly developed number and sex preference scales to more conventional adhoc measures and to social, economic, and demographic characteristics. c) Analysis of the relation of aspirations for children, traditional family values, religiosity, and life styles to fertility and contraceptive practice. d) A study of the factors influencing first use of contraception, choice of method, and subsequent use patterns. e) Mathematical models of the reproductive process to study births averted under various birth control regimes. f) Analysis of the long term fertility-contraceptive histories of women who accepted an intrauterine device early in the family planning program. Data for these studies come from the extensive material availble through the Taiwan household registration system, from special sample surveys, and from the records of the family planning program.